In general, a bone fixation screw apparatus is commonly used in orthopedics, neurosurgery, and the like to physically correct or fix the spine while being connected between adjacent vertebrae. A spin fixation procedure using the bone fixation screw apparatus is performed by a method of inserting a plurality of bone screws into the vertebrae, respectively, and connecting and fixing a rod disposed approximately in parallel to a longitudinal direction of the spine with the respective bone screws.
Such a bone fixation screw apparatus includes a bone screw insertable to the spine and a ‘U’-shaped receiving portion in which the rod is received. The bone screw may be provided as a single screw fixed to the receiving portion or a multi-axis screw capable of freely moving with respect to the receiving portion.
In use, when the bone screw is screwed onto the spine and the bone screw is accurately disposed, the rod is installed in each receiving portion to connect the bone screws. Thereafter, the rod is fixed by a fastening mechanism such as a fixing screw, a plug, or a similar form.
However, in a conventional bone fixation screw apparatus, deformation frequently occurs between the bone screw implanted in the bone and the receiving portion such that the bone screw is not firmly fixed and the stability is poor.
Further, the conventional bone fixation screw apparatus has a problem in that there is a technical limitation that a collet chuck or the bone screw having an outer diameter relatively larger than an inner diameter of the receiving portion is inserted together to one side of the receiving portion.
In addition, in the conventional bone fixation screw apparatus, since the bone screw has a single screw thread without considering the anatomical characteristics of the bone, there is a problem in that the bone screw is easily separated by the external force when the bone screw is implanted into the bone.
Accordingly, the need for the bone fixation screw apparatus is gradually increasing to firmly fix the bone screw to the receiving portion, easily fasten the collet chuck and the bone screw to the receiving portion, and prevent the bone screw from being easily separated by the external force when the bone screw is implanted into the bone.
The above information disclosed in the background art is only for enhancement of understanding of the background of the present invention and therefore, it should not be construed as the related art that is already known in the related art to those skilled in the art.